Calculating the Astronomical Unit (AU), Astronomers observed the Venus transit from various places. Because of the parallax effect, observers like A and B saw Venus's path shifted on the Sun's face. By trigonometry, this shift & the distance between the observers you can determine the distance to Venus. It's about 0.35 AU, so knowing the distance in miles, you can get the length of the AU in miles. Mona Evans, "Transit of Venus - Measuring the Solar System" http://www.bellaonline.com/articles Solar System, Mona Evans, Paths Shift, Astronom Observational, Secret Boards, Venus Paths, Astronom United, Sun Faces, Venus Transitional
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Captain Cook memorial at Venus Point, Tahiti. He headed an expedition sent by the Royal Society of England to observe the 1769 transit of Venus. This is where they did the main observations. (Photo: Frederick Sears) ©Mona Evans, “Transit of Venus – Captain Cook 1769” www.bellaonline.c...